There are at least 3 ways amateurs are different from professionals:
1. Amateurs take mistakes and failure personally ("I suck at this"). Pros don't take it personally ("my work sucks"). Failure is part of the process.
2. Amateurs practice until they get it right ("1 or 3 or 5 repetitions and then I'll move on to the next thing"). Pros practice until they can't get it wrong ("10 or 100 or 1000 repetitions or whatever it takes").
3. Amateurs are easily swayed from the plan by unforeseen life events ("I don't feel like practicing today"). Professionals adjust the plan constantly ("OK, if I can't practice in the morning, I will practice during my lunch break or in the evening or on the table when my family is asleep. Even for 15 minutes.")
The good and the bad news is that we have a pro and an amateur inside of every one of us. We only have to make this choice today. Tomorrow will be another battle.
[Thanks to John]